The present invention relates to a multiplexer system, and in particular, to a multiplexer system of voice and data communication in which a plurality of communication stations multiplex a plurality of kinds of information items into transmission block format so as to communicate information via transmission lines with a high transmission efficiency.
In a conventional system in which two stations connected via a transmission path are respectively provided with telephones and data terminals such that a voice from a telephone and data from a terminal are multiplexed on the transmission path so as to be communicated between the stations, the voice transmission takes precedence over the data transmission so long as there exists a voice input so as to send only voice information, namely, when the voice input is stopped, only the data is transmitted. As such a conventional multiplexed transmission system for voice and data communication, there has been known a system, as described in the JP-A-No. 59-225620, in which when a station on the transmission side does not effect a transmission, data is transmitted by using the overall frequency band of the transmission spectrum. This is accomplished by changing the bit rate of the data and the frequency of the carrier of the data in a modulator, and the change in the frequency of the carrier is detected by a station on the reception side so as to achieve a change-over to the mode for a reception of the data. In the conventional transmission system, however, also during a short period of time of a voice such as words uttered to chime in during a conversation, the transmission of the voice takes precedence over the data transmission, which results in a deterioration of the data transmission efficiency. Furthermore, according to the conventional system, since only data is sent in a period of time where the conversation is interrupted, the background sound received by each telephone is not transmitted to the communicating telephone during this period of time. Consequently, in the conversation, there intermittently appears a period of time where the voice of the partner of the conversation as well as the background sound cannot be heard, which leads to a problem that the speaker of the telephone feels a certain uneasiness.